1. Technical Field
This invention relates to munitions, and more particularly to a fuze for a munitions such as a grenades adapted to be deployed from mortars, artillery and rockets, and more specifically to a fuze mechanism having a construction adapted to ensure detonation once the mechanism is armed.
2. Discussion
Fuze mechanisms are used in a variety of military applications in connection with grenades deployed from mortars, artillery and rockets. A typical arming mechanism for such a grenade is shown in FIGS. 1 and 2. This arming mechanism of the fuze 10 includes a fuze housing 11 having an arming screw 12. The fuze housing 11 is secured to a grenade 32. The arming screw 12 has a threaded portion 14, which is engaged with a threaded opening 16a in an inertia weight 16. When in the unarmed state shown in FIG. 1, the firing pin tip 18 of the arming screw 12 rests within a bore 20 formed within a slide member 22. The slide member 22 is biased by a biasing spring 24 to the right in the direction of the drawing of FIG. 1. In the unarmed state, the firing pin tip 18 of the arming screw 12 located inside the bore 20 of the slide member 22 holds the slide member 22 in the unarmed and safe position shown in FIG. 1. Thus, the firing pin tip 18 is not able to engage a stab detonator 26 disposed in a recess 26a at the left end of the slide member 22 shown in FIG. 1, until the arming action of unthreading the arming screw threads 14 and the weight threads 16a occurs.
When the grenade is deployed, such as through a mortar shell, an artillery shell or a rocket payload, as the grenade falls to Earth, a drag ribbon 30 secured to the arming screw 12 unfurls and begins to vibrate and rotate. These drag induced dynamic movements of the drag ribbon 30 unthread the arming screw threads 14 from the weight threads 16a such that the firing pin tip 18 is withdrawn from the bore 20 in the slide member 22. The said movements are illustrated in FIG. 3. Upon release, the slide member 22 is urged to the right by the biasing force of the biasing spring 24, as also shown in the drawing of FIG. 3. This motion aligns the stab detonator 26 with the firing pin tip 18 of the arming screw 12. In addition to initiating the arming mechanism, the unfurled drag ribbon 30 also orients the grenade 32 during the grenade 32 descent phase of the deployed cargo flight. During deployed flight, the drag ribbon 30, lifts upward on the grenade 32 causing the grenade base 32a to be aimed at the surface of the ground 36 or target. When the base 32a of the grenade 32 strikes the ground surface 36 with the slide member 22 in the deployed and armed position, the inertial motions of the combination of the weight 16 and the arming screw 12 cause the arming screw 12 firing pin tip 18 to be driven into the stab detonator 26, thereby initiating the stab detonator 26 and functioning the grenade 32.
Owing to in flight oscillations of the drag ribbon 30 and the grenade 32 combined with irregularities in the ground surface 36, the grenade 32 may impact the ground surface 36 in a plurality of attitudes. It has been recently discovered that for a discrete population of the family of impacts, that the arming and firing mechanism is subject to failure. The fault mechanism and envelope can be characterized in the drawings of FIGS. 3 and 4. When the grenade base 32a of the grenade 32 contacts the ground surface 36 or target at small angles, as shown in FIG. 4, the fuze 10 can be momentarily disarmed. More specifically, if the grenade body 32 lands at an angle defined by xe2x80x9cxcex1xe2x80x9d, as indicated in FIG. 4, an upper surface 32b of the grenade 32 moves in one direction, in this example to the right (indicated by arrow 27) as the grenade 32 rotates about the contact point between the grenade base 32a and the ground surface 36, while the slide member 22 moves in the opposite direction or to the left as also shown in the illustration of FIG. 4.
This phenomena is a function of the spatial positioning between the ground 36 or target contact point, the grenade 32 center of gravity position at impact and the ability of the slide member 22 to move linearly relative to the fuze housing 11 and the top surface 32b of the grenade 32. The vertical plane for the specified performance fault illustrated in FIG. 4 thus lies between near zero degrees and xcex1 degrees, where xcex1 is the angle between the base 32a of the grenade 32 and a flat ground surface 36 which is perpendicular to the earth""s gravity vector as represented by the line 40 shown in FIG. 4. The fault envelope in the horizontal plane, as shown in FIG. 5, is zero degrees +/xe2x88x92xe2x80x9cxcex2xe2x80x9d degrees, where xcex2 is the angle between the highest point on the grenade upper surface 32b when the grenade 32 is oriented at some angle xcex1, from the ground surface 36 or target, and the longitudinal axis 34 of the slide member 22, and more specifically where the slide member 22, once deployed, is directed upward and away from the grenade base 32a impact point on the ground surface 36 or target surface.
When the grenade base 32a strikes the ground 36 or target surface at an angle xcex1 and the slide member 22 is positioned within the angle xcex2 on either side of the longitudinal axis 34, as defined in FIG. 5, the top surface 32b of the grenade 32 and the bottom surface 22a of the slide member 22 move in opposite directions. More specifically, in the drawing of FIG. 4, the top surface 32b of the grenade body 32 moves to the right while the slide 22 momentarily overcomes the biasing force of the biasing spring 24 and moves to the left. The relative motion between the top surface 32b of the grenade 32 and the slide member 22 causes the stab detonator 26 to be momentarily moved out of axial alignment with the firing pin 18 as the firing pin 18 is carried down toward the slide member 22 by the inertia of the arming screw 12 and weight 14. This momentary misalignment of the stab detonator 26 with the firing pin tip 18 of the arming screw 12 prevents the firing pin tip 18 from striking the stab detonator 26 or causes the firing pin tip 18 to strike the stab detonator 26 outside of its percussion sensitivity envelope, thus preventing initiation of the stab detonator 26 and detonation of the grenade 32. Finally, after dissipation of the relative velocities between the bottom of the slide member 22a and the top surface of the grenade 32b which had arisen from the instantaneous contact of the grenade 32 with the target or ground surface 36, the biasing force of the biasing spring 24 again causes the slide member 22 to be urged into its fully extended position shown in FIGS. 3 and 4. In this position the fuze 10 remains in an armed state, thus leaving the grenade 32 in a highly dangerous condition where external grenade 32 contact or vibration can cause the armed firing pin tip 18 to contact and initiate the stab detonator 26, thereby involuntarily functioning the grenade 32.
It is known, that in tactical maneuvers, large numbers of munitions incorporating a fuze mechanism 10 of the type illustrated in FIGS. 1-5 are not detonated upon impact with a ground surface 36 or target due to the orientation at which the grenade 32 impacts the ground surface 36 or target. It is therefore a principal object of the present invention to provide an arming mechanism for a munition, such as a grenade 32, which is not susceptible to spurious anomalies caused by the orientation at which the munition impacts a ground surface 36 or target when deployed.
It is still a further object of the present invention to provide an arming mechanism for a munition that incorporates a means to maintain the fuze mechanism in an armed state once the mechanism assumes an armed condition, regardless of the orientation or attitude of its associated grenade 32 when the grenade 32 impacts a ground surface 36 or target.
The above and other objects are provided by a fuze mechanism for a munition in accordance with the preferred embodiments of the present invention. In one preferred embodiment the fuze mechanism incorporates a fuze housing having an arming screw including a firing pin disposed therein. The firing pin engages within a bore in a slide member when the fuze is in an unarmed state.
The firing pin is moved out of engagement with the slide member during deployment of a munition as the arming screw is unthreaded from an internal component of the fuze mechanism. Once this occurs a biasing member urges the slide member laterally outwardly of the housing. Once the slide member moves to a fully extended position, a lock post carried in a bore formed in the slide member is partially released from the bore. In the partially released position, the lock post abuts an internal surface within the fuze housing to prevent the slide member from being urged momentarily out of the armed position should the munition contact a ground surface or target at an angle which would otherwise result in momentary disarming of the fuze mechanism.
The lock post does not add significantly to the cost of the fuze mechanism nor does it significantly complicate the construction or assembly of the mechanism. Instead, the lock post ensures that, once armed, the fuze mechanism remains armed regardless of the orientation at which the munition associated with the fuze mechanism strikes the ground surface or target.
Explosive Ordnance Personnel require deployed and armed fuzes to be rendered safe for handling and disposal. The unique design of the lock post allows for its manual defeat by inverting the fuze and grenade, and then over-riding the slide member biasing spring to the extent required to release the lock post, thus allowing the lock post to return to its original position in the slide member bore. With the lock post stowed in the slide member, the slide member can be returned to its safe position within the housing by compressing the biasing spring. The slide member may be secured in the safe position by re-threading the arming screw and weight, thus inserting the firing pin tip of the arming screw into the bore in the locking post to impede motion of the slide member in the deployed